UNIX Network Programming Volume 1, Third Edition [Electronic resources] : The Sockets Networking API نسخه متنی

27.4 IPv6 Extension Headers

We do not show any options with the IPv6 header in Figure A.2 (it is always 40 bytes in length), but an IPv6 header can be followed by the following optional

extension headers :

1. Hop-by-hop options must immediately follow the 40-byte IPv6 header. There are no hop-by-hop options currently defined that are usable by an application.

2. No destination options are currently defined that are usable by an application.

3. The routing header is a source routing option, similar in concept to what we described for IPv4 in Section 27.3.

4. The fragmentation header is automatically generated by a host that fragments an IPv6 datagram and then processed by the final destination when it reassembles the fragments.

5. The use of the authentication header (AH) is documented in RFC 2402 [Kent and Atkinson 1998b].

6. The use of the encapsulating security payload (ESP) header is documented in RFC 2406 [Kent and Atkinson 1998c].

We said the fragmentation header is handled entirely by the kernel, and the AH and ESP headers are automatically handled by the kernel based on the SADB and SPDB, which are maintained using PF_KEY sockets (Chapter 19). This leaves the first three options, which we will discuss in the next two sections. The API to specify these options is defined by RFC 3542 [Stevens et al. 2003].